indeed, if you want a 100% open source 4G network, you can use srsLTE for the eNodeB, and open5gs for the EPC. No proprietary bits needed, and no non-free licenses needed either.
Please note: OpenAirInterface is not open source software. Large parts of it (particularly everything related to the RAN) are under a license that does not comply with either DFSG, nor OSI Open Source Definition, nor the FSF Free Software Definiton.